Field of Invention
The present invention relates to a phosphor, a light emitting apparatus including the phosphor, and a method of forming the phosphor.
Description of Related Art
The light emitting diode (LED) is a mercury-free environmental friendly light source with advantages, such as low power consumption, high service life, fast response speed, no heat radiation and small volume. In 1996, the technology, which uses a blue LED with yttrium aluminum garnet (YAG) yellow phosphor together to generate a white light, was firstly issued by Nichia Corporation of Japan, and thereafter the white light emitting diode (WLED) has been formally commercialized. Due to the flourish development of the related technical industries in recent years, the luminous efficiency and the reliability of the WLED product have been increased continuously. Therefore, with the development trend of energy conservation and carbon reduction, the WLED, referred to as a green energy light source, is expected to gradually replace the conventional lighting apparatus such as an incandescent bulb, and will be used widely in industries, for example, general apparatus, displayer, automobile, electronics and communications.
The white light emitted by the WLED is a two-wavelength light, three-wavelength light or four-wavelength light as a result of a mixture of multiple colors. At present, the manufacturing method of WLED includes: exciting a yellow phosphor with a blue LED; exciting a red phosphor and a green phosphor with a blue LED; exciting phosphors of multiple colors with a purple LED or a UV LED (e.g., the disclosure of Patent I340480 of Taiwan); using two to four kinds of LEDs to mix emitted light thereof to form a white light by adjusting individual brightness of the LEDs; and so on. The WLED which is manufactured by using the blue LED to excite the YAG phosphor to generate a yellow light and then mixing the yellow light and the blue light to generate a white light still has become a mainstream on the market due to its low cost and high efficiency. However, the color rendering of the WLED is incomparable with the conventional bulb and the power saving bulb. Therefore, a red phosphor should be added in order to realize a warm white light LED. When the blue LED is used together with the red phosphor and the green phosphor, both the color temperature and the color rendering are improved and the efficiency is also good.
The phosphor is a common luminescent material, wherein an inorganic phosphor generates a fluorescent light through electron transition. When the phosphor is excited by the light, the electrons in the phosphor are excited to the excited state of the high energy level and then the electrons return to the original low energy level state. At this time, the energy is radiated in the form of light. The inorganic phosphor is mainly constituted by a host lattice and an activator. Sometimes, if necessary, a co-activator or a sensitizer may be added to facilitate the luminous efficiency. The activator is used as a luminescence center while the host lattice delivers energy during the process of excitation. If a combination of the host lattice and the activator is changed the wavelength of the light emitted by the phosphor can be changed so as to generate different luminescence colors. In addition, the chemical composition of the host lattice, the type and concentration of the activator and other factors all can affect the luminous efficiency of the phosphor. The development of the fluorescent material is from the early-stage unstable sulfide to the later silicon oxide (silicate) fluorescent material which has a good chemical stability. In recent years the nitride/oxynitride fluorescent material is very popular.
At present, the typically phosphor includes an aluminum oxide phosphor, a silicon oxide phosphor and a nitride/oxynitride phosphor and so on. The Ce-doped YAG phosphor (mainly constituted by Y3Al5O12:Ce) provided by Nichia Corporation of Japan in 1996, the TAG phosphor (mainly constituted by Tb3Al5O12:Ce) provided by OSRAM GmbH of Germany in 1999 and the phosphor disclosed by Patent I353377 of Taiwan all are aluminum oxide phosphors using Ce as the activator. Moreover, Ba2MgSi2O7:Eu phosphor provided by GE Company of U.S. in 1998 and the phosphor disclosed by Patent I306675 of Taiwan using Ce, Eu, Mn and so on as the activator and so on are silicon oxide phosphors. In addition, since the nitride and the oxynitride have excellent performances, such as good thermal stability, good chemical stability, nontoxicity and high strength, the phosphors which use the nitride and the oxynitride as the host lattices are also published gradually, such as the disclosures of U.S. Pat. No. 6,649,946, U.S. Pat. No. 6,632,379, U.S. Pat. No. 7,193,358, U.S. Pat. No. 7,525,127 and U.S. Pat. No. 7,569,987 and U.S. Patent Publications US 2009/0309485 and US 2006/0175716. However, in the general nitride/oxynitride phosphor, if Tb (Terbium) ion is used as the activator, its applicable value is always affected by the problems, such as the poor luminous efficiency and the absence of adjustability for the light color caused by a narrow emission band. Therefore, it is still needed to research and develop a phosphor which can overcome the disadvantages of the conventional technology and has a high applicable value.